Pete Garcia has published some really weird, unbiblical stuff in the past. I've called him out on a few things he's written about because he uses scriptures that aren't remotely related to the topic at hand. While a lot of his stuff appears to make sense, you really have to delve deep into what he's saying to really figure him out.
All that to say, yes, UFOs could be used as the excuse for why millions of people go missing, but if you're asking me if there really are aliens (other than the illegal aliens coming across the southern border), it's an unequivocal "no."